In a fluid rotary machine, e.g., air feeding pump, liquid feeding pump, a reciprocally-driving mechanism in which a fluid is repeatedly sucked and discharged by a reciprocal movement of a piston unit linked with a crank shaft rotating along with rotation of a main shaft has been employed. On the other hand, the applicant of the present application has proposed a modified fluid rotary machine in which a fluid is repeatedly sucked and discharged by linearly reciprocally moving double-headed piston units, which are mutually intersected and attached to a crank shaft with an eccentric cam, on the basis of the hypocycloid principle. Rotary valves, each of which switches between a fluid sucking action and a fluid discharging action for each of cylinder chambers, are disposed coaxially with the main shaft, and pipes connected to intake ports and discharge ports of each of the cylinder chambers are summarized, so that number of external pipes can be reduced and an installation area of the machine can be reduced (see Patent Document 1).